Twin Cam front suspension geometry different than S2?

[TurboFource]

It appears the front suspension geometry on a Twin Cam chassis is different than an S2 based on the drawing for an S2.

I measure 31.0" vs 30.360" for upper distance between points
25.125" vs 24.660" between lower points
8-7/8" vs 9.0" for the lower point from top of the frame

TC measurements listed first....done with a tape measure but within less than 1/64" (.015) error

Nothing is bent and it diagonal dimensions are identical.

Was this done when they raised the ride height to meet Fed regs

[MRN I J]

I once plotted the camber change on my S2 just to see how my tyres were going to behave on the car in roll, figures long gone now

[gideon]

Turbo - this article gives some explanation of the things they changed for the Twin Cam, straight from the horses mouth too.

https://drive-my.com/under-the-skin-of-the-lotus-europa-twin-cam/

[TurboFource]

Thanks Gideon! They did change the geometry.

[jbcollier]

They changed the ride height at the front and then lowered the floor for more headroom.  Geometry-wise, suspension arms fit across the range with the exception of the S1 and early S2 upper rear arms.

[TurboFource]

I now read that Lotus also changed steering rack spacers on the Twin Cam and Special to improve bump steer in addition to suspension geometry changes. So does a Twin Cam handle better than the S1/S2? Any skidpad numbers available?

[jbcollier]

The S1/2 extend the rack by adding spacers at the outer tie rod end.  The TC/S use spacers to extend the inner tie rod end out to where it is roughly inline with the a-arm pivots.  In the straight ahead position, this reduces bump steer.  This is important in racing but less so on the road.

With identical tires, the S1/2 would give higher skid pad numbers due to being lighter than the TC/S.

[TurboFource]

Thanks JB

[MRN I J]

The S1/2 extend the rack by adding spacers at the outer tie rod end.  The TC/S use spacers to extend the inner tie rod end out to where it is roughly inline with the a-arm pivots.  In the straight ahead position, this reduces bump steer.  This is important in racing but less so on the road.

With identical tires, the S1/2 would give higher skid pad numbers due to being lighter than the TC/S.

So the spacers screw on to the rack bar & extend the ball joint position, by how much JB

[jbcollier]

Good question, don't know for sure.  Would assume they extend the same amount as the S1/s ones.

[dakazman]

   Thanks guys for bringing up a subject I really never heard of. Reading through a list of Google hits I found myself being drawn into being a wheel man and not a builder. Having driven literarymadness’s car I loved the handling in a turn.  My entire suspension is in place but not setup or serviced.  I will not race mine or test the limits so what should one , as a builder shoot for? 
  My only suspension / steering problem was on my corvette.  having the power steering shims set to high  and  when driving went lock to lock in a slight motion. Fun at 40mph in 2nd gear 🤪

Dakazman
 
 
 

[GavinT]

Years ago I cut 'n' shut an S2 rack to remedy the bump steer. Only later did we discover the TC/S used longer rack sleeve nuts to achieve the same thing.
The added rack length provided on the TC/S is about 3.25 inches in total, so reasonably substantial. I don't have precise measurements to hand.

It's also possible to raise the stock rack to effect a similar result but that requires the rack mounts be positioned horizontally as distinct from their stock vertical mounting on the front of the T.
The internal metal work kinda gets in the way, otherwise. Shims are used to attain the final position and equalise both sides.